Muons are elementary particles similar to the electron and belong to the lepton group of elementary particles. Their mass is about 207 times greater than that of the electron, and the average energy of muons reaching the Earth's surface (with a flux of about 1 muon per square centimeter per minute) is about 4 GeV. These particles are continuously produced in the upper layer of the atmosphere by the nuclear interactions of high-energy primary cosmic-rays with atmospheric nuclei. Muons are unstable and decay into electrons and neutrinos with an average lifetime of 2.2\(s\) . However, because of the large time-dilation effect due to their high energies, they can reach the Earth's surface and, depending on their energy, can penetrate large thicknesses of material. The particular mass of muons (intermediate between an electron and a proton) causes a negligible probability of producing electromagnetic cascades and relatively low energy losses due to ionization, two properties that together with the absence of strong nuclear interactions make them a good tool for imaging large-scale structures on Earth. To exploit this natural atmospheric muon flux, the technique of muography (or muon radiography/tomography) was developed in a similar way to X-ray radiography [1]}.
This technique has been used for various applications, from the study of hidden chambers in pyramids [2]} to the inspection of the density distribution or internal structure of objects such as volcanoes [3]} and nuclear reactors [4]}, taking into account the absorption of muons in the volume of interest. Following recent developments in the field of detectors, research groups have attempted to build various portable and small muography detectors (see e.g. [5]}). This has led to thinking about new applications of muography, such as using muons as a tool for infrastructure inspection [6]}. In addition to the above applications, cosmic-ray muons have been introduced as a candidate for homeland security and national border inspections by considering the multiple Coulomb scattering of muons in matter, especially in high-Z materials such as nuclear materials [7]}.
